1. Field of the Invention
The present invention relates to a support unit suitable as a support bearing of a precision ball screw used in a feed gear for a numerical control machine tool, precision measuring equipment, and the like.
2. Description of the Prior Art
Prior art support units of this type are structured, for example, as shown in FIGS. 3 and 4. In the support unit shown in FIG. 3, a single angular ball bearing A is assembled in a housing 1 to receive a thrust load in one direction. A shoulder 2 is formed in an inner peripheral surface of the housing 1. A step portion 3A is provided on a shaft 3 serving as a supported shaft so that one end of an outer race 5 of the angular ball bearing A fitted in the housing 1 is held by the shoulder 2 and one end face of an inner race 6 is in abutment with the step portion 3A thereby to receive the thrust load.
In the support unit shown in FIG. 4, two angular ball bearings A1 and A2 are assembled to receive thrust load in two directions. A shoulder 2 is formed in an inner peripheral surface of a housing 1A having the two angular ball bearings A1 and A2 fitted therein to hold an outer race 52 of one bearing A2. A bearing pressing cover 8 is fixed to an open end of the housing 1A to hold an end of an outer race 51 of the other bearing 1A at an end face 9 of the cover 8 thereby to receive the thrust load.
Although the support units mentioned above are of an open type and no seal structure is involved, a seal structure is employed in some cases in order to seal lubricant therein and to achieve a dust proof condition. In this case, in the support unit shown in FIG. 3, a sealing cover 10 is provided, as shown by a chain line, and furthermore, a seal structure is employed in the housing 1. Alternatively, seal members or oil seals 11 are attached to the cover 10 and the housing 1. In the support unit shown in FIG. 4, a seal structure is employed in the bearing pressing cover 8 and in the housing 1A. Alternatively, the seal member or the oil seal 11 is employed. Reference numeral 12 designates a lock nut.
However, in the prior art mentioned above, since the bearing is held at the inner surface of the housing 1, the structure is complicated. In particular, when the support unit is used with high precision and high rigidity by applying a preload to the bearing A, there exists a problem in that high machining accuracy is needed in forming the shoulder 2 in the inner peripheral surface of the housing 1 or 1A. Accordingly, high productivity is difficult to achieve.
Furthermore, when the bearing pressing cover 8 or the sealing cover 10 is provided at the opening end of the housing 1 or 1A, a problem is involved in that the number of parts and costs are increased.
Moreover, when the seal structure is employed, a problem is posed in that the structure of the housing 1 or 1A becomes complicated since the sealing member and a seal are attached to the housing 1 or 1A, and the attaching of the sealing member is troublesome.